Enteric coating solutions that require organic solvents have been used in the past. However, because of the problems associated with the use of organic solvents (i.e., pollution of the atmosphere, safety and hygiene problems for workers, danger of fire and explosion, and expensive equipment requirements to limit or reduce the danger of fire or explosion), aqueous enteric film coating suspensions, such as the COATERIC enteric film coating system of Colorcon, West Point, Pa., were developed. The COATERIC system is disclosed in Colorcon U.S. Pat. No. 4,556,552, which issued on Dec. 3, 1985, and in Colorcon U.S. Pat. No. 4,704,295 which issued on Nov. 3, 1987, both of which are incorporated herein by reference.
Other known aqueous enteric film coating systems include an aqueous dispersion of acrylic resins, for example, polymethacryl methacrylate copolymer, and dispersions of acetates, for example, cellulose acetate phthalate.
A problem associated with the known aqueous enteric coating suspensions is tackiness of the coating.
Another problem with the known aqueous enteric coating systems is that they require at least three processing steps to form the enteric coating suspension. For instance, with the EUDRAGIT system, plasticizer, antifoam, and talc are mixed stepwise into the EUDRAGIT dispersion. With the AQUATERIC-celllulose acetate phthalate dispersion system, the AQUATERIC powder is dispersed in water, followed by stepwise addition of plasticizer, and Tween 80 to form the AQUATERIC suspension. With the COATERIC system, the COATERIC powder, an antifoam, and ammonium hydroxide are mixed into water to form the COATERIC suspension. The need for three processing steps is a drawback because the more processing steps there are, the higher the chances of processing error occurring.
In the Colorcon U.S. Pat. Nos. 4,556,552 and 4,704,295, Colorcon's COATERIC non-toxic edible enteric film coating dry powder, which comprises polyvinyl acetate phthalate (PVAP), a water-soluble plasticizer, an auxiliary film-forming suspending polymeric agent for the PVAP, and pigment particles, is mixed into water, and after the enteric dry powder is thoroughly wetted, an ammonium hydroxide solution is added to form an enteric coating suspension. Although the COATERIC coating suspension forms a very good enteric coating, the COATERIC suspension has the smell of ammonium hydroxide.